Radio tube mount



Sept. 5, 1939. J. M. POMFRETT RADIO TUBE MOUNT Filed Oct. 21,1936

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INVENTOR B A I XTTb-Z liclfl Patented Sept. 5, 1939 UNITED STATES PATENT OFFICE RADIO TUBE MOUNT Application October 21, 1936, Serial No. 106,787

2 Claims.

This invention relates to electron discharge tubes and more particularly to such devices as radio tubes and the like.

An object of the invention is to provide a radio tube mount-or the like with a. novel form of electrode spacer whereby tube noises are materially reduced.

A feature of the invention relates to a radio tube mount of the type having one or more wirewound grids, the grids being held in place by an improved insulator spacer member.

Another feature relates to the novel organization, arrangement and relative location of parts which go to make up an improved mount for a radio tube and the like.

While the invention will be described herein as embodied in one particular kind of radio tube it will be understood that this is done merely for explanatory purposes and not by way of limitation. Accordingly in the drawing,

Fig. 1 is an elevational view, partly in section, of a radio tube embodying features of the invention.

Fig. 2 is a sectional view of Fig. 1 taken along 5 the line 22 thereof.

Fig. 3 is a detailed view of a modification of Fig. 1.

Fig. 4 is a top plan View of Fig. 3.

Fig. 5 is an end view of Fig. 4.

30 Fig. 6 is a sectional view of a modified form of spacer according to the invention.

Fig. 7 is a sectional view of a still further modification of spacer.

Referring to- Fig. l the numeral I represents 5 any conventional form of enclosing envelope such as customarily employed in radio tubes, which is provided with a stem or header 2 into which are sealed the various lead-in and support wires 3 to H inclusive.

40 The electrode assembly may comprise an electron emitting cathode |2 which is shown in the drawing as of the indirectly heated type, although other well-known forms of cathodes may be employed. The cathode sleeve which carries the 45 emissive coating is connected to the lead-in wire 6, and the cathode heater is connected to the lead-in wires 1, 8. Surrounding the cathode is a series of grids each consisting of a pair of siderods around which a fine grid wire is disposed,

50 each turn of the grid wire being conductively fastened to the side-rods. Thus the grid wires |3 are disposed around and fastened to the siderods |4, I5, and the grid wires I6 are disposed around and fastened to the side-rods I8. Sur- 55 rounding both grids is a tubular metal plate or anode l9 fastened to the side-rods 2|), 2|. The various side-rods are welded or otherwise fastened to the respective lead-in and support wires as shown. Preferably the Various electrodes are spaced apart by upper and lower insulator spacer 5 discs 22, 23 respectively, of mica or other suitable insulation, it being understood that each disc is provided with appropriate perforations through which the various side-rods protrude. The spacer discs are prevented from sliding off the side- 10 rods by suitable lugs or small projections 24 formed on the plate side-rods 2| 2|.

It is the usual practice to assemble the spacer discs on the side-rods so that they engage the end turns of the grids, thus preventing longitudinal 15 movement thereof. I have found that when the grids are in the form of helically wound wires, the direct contact between the end turns and the mica spacers is the cause of much tube noise. Furthermore since all the electrodes are in direct 20 contact with the spacers there may be considerable leakage therebetween. In accordance with the present invention this leakage is materially reduced by reducing to a practical minimum the direct contact between the end turns of the grids and the upper and lower mica spacers. Thus as shown in Figs. 1 and 2 there is interposed between each mica spacer and the grid ends a narrow strip 25, 26 of suitable insulation material. These strips are preferably smaller in width than 30 the diameter of the first grid l3 but are preferably sufficiently long to extend entirely across the adjacent spacer discs, as shown clearly in Fig.

2. Each strip is provided with a set of perforations equal in number to the perforations in the spacer discs, so as to allow the said strips to be positioned over the Various side-rods. In assembling the mount, the lower strip 26 is positioned on the side-rods, then the spacer 23 is placed in position and the tabs or lugs 24 are applied. The strip 25 is placed in position, and then the upper spacer disc 22 is assembled in place and is forced down on the side-rods until the grids engage the two strips 25, 26, whereupon the tabs 24 may be applied to hold the parts together. Preferably each of the strips 25, 26 before being assembled on to the mount is provided over its entire surface with a coating of a ceramic insulating material such for example as aluminum oxide, beryllium oxide or the like.

While it is not necessary to fasten the discs and strips together, in certain types of tubes this may be advisable. Thus as shown in Fig. 3 the upper disc 22 may be fastened to the side-rods 20, 2| by wire clips or tabs 21, 28 in the manner described in detail in Patent No. 2,075,761, granted March 30, 1937. These tabs may also extend through the strip 25 to fasten the same integrally to the disc 22. 'It will be understood that any other method of fastening the members 22 and 25 together may be employed.

In certain types of tubes it may be preferable to employ spacer members of ceramic material, thus as shown in Fig. 6 the spacer member 29 is in the form of a ceramic body having a series of perforations 30 to receive the various siderods. With this type of spacer it is possible to mold or otherwise form it with an integral narrow ridge or strip 3| adapted to perform the same functions as the strips 25, 26. In this embodiment, since the spacer material is a refractory ceramic itself, it is not necessary to provide it with a separate coating of such material.

Instead of molding the strip portion 3| with a flat face, it may be molded with a V-shaped face as shown in Fig. 7 to further reduce the possibility of leakage between the electrodes.

Various other changes and modifications may be made without departing from the spirit and scope of the invention.

What I claim is:

1. A radio tube mount including a central cathode a first grid immediately surrounding said cathode, a second grid surrounding the first grid, an insulator spacer member for spacing the grids and cathode, and a mica strip interposed between said spacer and the end turns of said grids to space said end turns from said spacer member, said mica strip having its exterior surface provided with a coating of refractory insulation material and having a width materially less than the diameter of said first grid and contacting the end turns thereof.

2. A radio tube mount including a cathode and a grid electrode having a series of wire turns immediately surrounding said cathode, a spacer member for spacing said cathode and said electrode, and a narrow strip of insulation interposed between the end turn of said electrode and said spacer, said strip engaging said end turn to space it from said spacer, said strip having a width materially less than the diameter of said electrode and contacting the end turn thereof, both said spacer member and strip being of mica with the strip having a. coating of a refractory insulation material.

JOHN M. POMIE'RETT. 

